Flotation machines are commonly used to separate solid materials by agitating fluid containing the desired material. An impeller located in the flotation cell creates the agitation and aerates the fluid, thus dispersing air contained in the pulp so that air bubbles develop to which the particles of the material being separated stick. As the particles rise with the air bubbles to the surface, a froth byproduct forms on the surface and has a higher concentration of the floatable material, as compared to the starting product.
Flotation cells can be used to separate crushed ore, sewage or many other products, as long as one of the products is floatable, i.e., can stick to the air bubbles.
Conventional flotation cells primarily make use of large, cumbersome horizontal drive belt arrangements which are connected to expensive low-speed electric motors. Shaft-mounted vee-belt drives are commonly employed and are driven by electric motors connected via drive belts. Other systems include shaft-mounted horizontal gear reducers with vee-velt drives and fixed-speed gear motors. All of these systems have various drawbacks.
Such conventional flotation cells are incapable of a soft start, but rather change abruptly from an inoperative state to full speed. None of these systems has variable speed capability, and thus are incapable of being tuned to the feed characteristics at which the liquid being inputted is fed into the flotation cell. The complex belt structures of the conventional flotation cells, and the expensive electric motors, require significant maintenance and considerable part replacement due to wear. Conventional cells have multiple drive belts, large sheaves, large drive guards, motor mounting brackets and bearing housing mounting brackets, all of which increase the expense and complexity of the flotation cell systems. Furthermore, most conventional drive systems for flotation cells include radial bearing loads; bearings, seals and housings are large, and consequently have a greater likelihood of breakdown, are more expensive and need more maintenance. Finally, it is very difficult to run conventional flotation cells under computer control to monitor or vary the rotor speed torque and energy consumption.
For example, U.S. Pat. No. 5,039,400 relates to a flotation machine for floating minerals from slurries containing minerals in particulate form. The flotation cell includes a mixing mechanism which has a stator and a rotor. The rotor is attached to a hollow axis which is geared with bearings to the supporting structures of the cell. An electric motor rotates the axis through intermediate cone belts. Such a flotation device suffers from the previously described drawbacks, namely it utilizes expensive low-speed electric motors and complicated belt driving mechanisms, and furthermore, is incapable of a soft start, and fails to permit an operator to vary the speed to match the performance to changes in feed characteristics.
Another apparatus is shown in U.S. Pat. No. 4,043,909 which is an apparatus and method for solidification of sludges. The apparatus includes a driving means which includes a prime mover such as a hydraulic motor and reduction gear. This reduction gear includes four output shafts, each of which is connected to an agitating shaft through a bearing, and a shaft coupling. While U.S. Pat. No. 4,043,909 does not require the use of belts, the inclusion and utilization of the complex reduction gear system requiring multiple output shafts, agitating shafts, bearings and couplings, adds to the complexity and expense, further requiring greater downtime for maintenance and increases the frequency of wearing down of parts. Furthermore, the system is not capable of soft starting or speed variance over a large range.